Semi-Active Laser (SAL) guided missile systems are used when destruction of a specific target requires precision. In some cases, such precision is needed to minimize collateral damage. In some cases, such precision is desired to ensure that a high-value target is successfully destroyed.
The principle of operation of SAL guided missile systems is to “paint” or designate a target with a signal that is perceivable by a missile. A system called a seeker is responsible for perceiving the signal reflected by the designated target. A forward positioned operator may paint the desired target using a Laser Target Designator (LTD), for example. An LTD can have a Short-Wave Infrared Radiation (SWIR) laser to generate a sequence of laser pulses to be used to paint the target. The sequence of pulses can have a Pulse Repetition Interval (PRI) or a Pulse Repetition Frequency (PRF) that can function as a signature of the LTD.
The seeker of the SAL guided missile can be equipped with a SWIR detector, which can be configured to detect SWIR signals and to determine whether the detected SWIR signals have a PRI corresponding to the LTD. The seeker can be matched or paired with a specific LTD by configuring both the LTD and the seeker with the same PRF/PRI. If the SWIR detector determines that the detected SWIR signals have the PRI signature of the LTD, then the target from which the detected signal is reflected is deemed to have been designated by the LTD. The seeker then can sense this reflected designation signal and also can determine the direction of the target relative to the guided missile. The seeker may output a signal indicative of the determined direction for use by a guidance system on the missile. The missile's guidance system then can direct the missile to the designated target.
Some seekers also have a passive Imaging InfraRed (IIR) target location system in addition to a SAL target location system. Such seekers are sometimes called dual-mode seekers. The passive IIR target locator can include an infrared camera to capture images of a scene that includes the target designated by the LTD. Image features corresponding to the designated target can be identified. Image coordinates of the identified features within the captured images can be used to determine the direction of the target relative to the missile. Reliable identification of imaged target features, however, can be performed only when the target features are imaged by a sufficient number of pixels in an imager. The number of “pixels on target” increases as the range closes between the missile and the target. The signal strength of the ambient infrared light emitted from and/or reflected by the imaged scene can be much lower than the signal strength of the pulsed laser signal generated by an LTD and reflected by the target. Thus, target detection and location using an IIR-mode of operation can be performed when the range between the target and missile is relatively close. For long-range target detection and location, SAL-mode operation can be better used, due to the relatively high signal strength of the LTD laser signal.
A dual-mode guided missile can be launched by a launching vehicle that is located a great distance from a desired target. The dual-mode seeker of such a launched missile might first acquire a target using the SAL-mode of target detection and location, due to the relatively large signal strength of the LTD laser signal. When the range to the designated target closes to a distance at which the passive IIR-mode of target detection and location can be used, the seeker can switch modes to the IIR-mode of operation.
Although the forward positioned LTD operator is no longer required to continue painting the target after the dual-mode missile has switched to the IIR-mode of operation, the forward positioned LTD operator often has no way of knowing this. The forward positioned LTD operator often is totally ignorant of the missile's mode of operation. The forward positioned LTD operator then continues painting the target until the missile strikes the target. There is a need for the forward positioned LTD operator to be permitted to disengage the target at the earliest time possible. If the LTD operator were made aware of when the guided missile transitions from the SAL-mode to the IIR-mode of operation, he/she could suspend the painting of the target, and perhaps could evacuate the forward position, even before the missile strikes the designated target.